KR100384432B1 - Ceramic slip composition and its manufacturing method - Google Patents

Abstract

A uniform suspension of ceramic powder and method for making the same. The suspension is prepared by mixing finely divided ceramic powder in an aqueous carrier fluid, combining with a dispersing agent, and alternatively, an organic binder when forming a slip. The ceramic powder has an average particle size of about 0.5 micron or less and is present in the suspension in a loading of up to 30% by volume of the total solids in suspension. A passivating agent is present in the carrier fluid in an amount of 0.5 to 5% by weight of the ceramic powder present for suspension and slip respectively. After the addition of a dispersant, the suspension has a Bingham yield point of less than 230 dynes/cm2 and an apparent viscosity of less than 3000 cps. A green layer produced from the slip exhibits a pore size of less than 0.5 micron.

Description

Ceramic slip composition and its manufacturing method

Field of invention

The present invention relates to improved aqueous ceramic suspensions, slips and ceramic green bodies and methods of making the same. In particular, the present invention relates to the use of an optimum range of surface stabilizers and dispersants in an aqueous suspension of finely divided ceramic powder.

Background of the Invention

Multilayer capacitor (MLC's) manufacturers are increasingly aware of the importance of manufacturing thinner dielectric layers due to consumer demand for reduced size and cost. These capacitors are typically produced by co-burning, ie, sintering the ceramic dielectric composition and conductive electrode material at an temperature in the range of about 1000 to 1400 ° C. in an oxidizing atmosphere.

Dielectric layers have traditionally been prepared by preparing ceramic powder suspensions in liquid vehicles containing dispersants, and then adding organic resin matrices that serve to bond the ceramic particles in the suspension. Various methods are known for applying a suspension and binder mixture (hereinafter defined as slip) to a substrate to form a very thin layer of suspended solids. Methods such as wet coating, tape-casting or doctor-blading are well known to those skilled in the art. The dried thin layers, commonly referred to as green layers, can then be coated with a conductive electrode and laminated together with similar layers to produce a green body. Subsequently, the laminate is trimmed and co-fired to alternately stack the sintered electrodes and dielectric layers, and finally a structure is formed to form a finished capacitor by attaching a lead wire to the end of the end. Conventionally, both aqueous and organic liquids have been used for the suspensions used in the dielectric compositions, but due to environmental and safety concerns, there is an increasing tendency to use aqueous suspensions for the preparation of dielectric layers.

Another tide in the capacitor industry is to make thinner dielectric layers to get more capacitance per unit volume. Thus, the thickness of the dielectric layer has been reduced from 25 microns (25 microns) to 10 microns (10 microns). The goal now is to reduce the thickness to 5 micrometers (5 microns) or less. These thinner layers need to use extremely small solid ceramic particles in the suspension to achieve the required high density and fine particle size in the final burned layer. Reducing the ceramic powder to these small particle sizes, i.e., less than 0.5 micrometers (0.5 microns), tends to have significant soluble portions that dissolve in aqueous suspensions and cause chemical reactions with dispersants and binders in solution.

Smaller particles are also more difficult to handle, making the automation system inadequately complex and expensive.

Because of the dielectric properties, barium titanate selected as the base material of the capacitor composition forms soluble cations. Since the binder contains a dispersant, any reaction of the soluble cation or its accompanying hydroxyl ions with the chemical dispersant in the binder may result in "salt" or precipitation of the aggregates of the binder and the metal cation-dispersant complex. These complexes or agglomerates often create voids in the ceramic body during the binder combustion step prior to sintering, which can increase leakage levels or cause electrical short circuit paths. Pore formation should not occur particularly in layers having a thickness of less than 10 micrometers (10 microns).

Another problem that arises when preparing suspensions from ceramic powders with diameters of less than 0.5 micrometers (0.5 microns) is that both the interface area between the solid and liquid carrier and the number of particles in a given volume are greatly increased. This leads to high physicochemical interactions between the solid particles in the liquid phase and, in particular, decreases in processability even at commercially acceptable solids content. Thus, it can be expected that the benefit of finer particle size can be offset by the need to lower the suspension or slip coarse content. The production process of exposing the suspension to high shear conditions such as encountered during pumping or tape casting causes excessive gelling and in the worst case an expansion that is characterized by an unprocessable suspension with thickening properties and high viscosity by shearing ( dilatant).

Various attempts have been made to prepare fine ceramic powders in aqueous suspensions and slips. For example, US Pat. No. 3,496,008 describes ball milling ferroelectric materials such as barium titanate such that the milling material content in water is 60% by weight solids. The mixed suspension is rediluted to have the desired consistency for spray application.

EP 0 532 114 discloses a process for the preparation of an aqueous ceramic suspension comprising finely divided ceramic particles, a dispersant and, if necessary, a polymeric binder and a softener. The method includes steps that can be performed separately or together to delay reaggregation of the ceramic particles. The ceramic powder suspension was described with a maximum stability of 73 hours. This period includes (i) prefiltration and washing of the ceramic particles, (ii) adding oxalate to the suspension, (iii) CO ₂ exclusion step, (iii) cooling step, and / or (iv) addition Obtained by performing one or more of the dispersion steps.

U. S. Patent No. 3,551, 197 prepared a dielectric composition from 40 to 90 wt% ceramic powder with water vapor. The ceramic powder is selected from the group comprising barium titanate, strontium titanate, calcium titanate, and lead titanate, and has a particle size of 0.5 to 3 micrometers (0.5 to 3 microns). Suspended ceramic material is combined with a binder such as, for example, polymethylene glycol or diethylene glycol.

In US Pat. No. 4,968,460, an aqueous emulsion of a water soluble polymer binder is mixed with an aqueous suspension of ceramic material at a solids content of at least 50% by weight. The polymeric binder is used in the range of 0.5 to 35% by weight, optionally with up to 5% by weight of the selected dispersant. The tape made from the slip composition has a thickness of 30 micrometers (30 microns) to 2.540 mm. Particle sizes ranging from 0.5 to 12 microns (0.5 to 12 microns) are disclosed.

However, these references do not address the problems encountered in the manufacture of aqueous suspensions or slips of ceramic powder having particles less than 0.5 micrometers (0.5 microns) in diameter.

Suspended in an aqueous carrier fluid for a long period of time and substantially less than 30 dyn · s / cm 2 (3000 centipoise (cps)) without solidification as measured at high shear rates of 50 to 100 / sec. Suspensions of ceramic powders with diameters of 0.5 micrometers (0.5 microns) or less that maintain an apparent viscosity can be desirable improvements in the field of ceramic suspensions, slips, and methods for their preparation.

Another object of the present invention is to prepare an aqueous suspension having a ceramic powder content of up to about 30% by volume and having an apparent viscosity of less than 30 dyn · s / cm 2 (3000 cps).

It is still another object of the present invention to stabilize the surface of the particles constituting the ceramic powder using ultrathin layers of relatively insoluble surface stabilizers such as barium oxalate against soluble anions and cations, and then add a dispersant to provide a stable suspension. To manufacture. Surface stabilization is essential to prevent the interaction of barium or other ions that can crosslink with the dispersant.

It is a further object of the present invention to provide about 30% by volume of the total solids, having a viscosity low enough to impart the good fluidity needed to produce the untreated thin layer, containing the binder required to produce the tacky film and having a uniform distribution of ceramic particles ( 70 wt%) or higher solids content to make it possible to produce stable slips of barium titanate.

Another object of the present invention is to provide a slip that is non-expandable even under high shear forces such as pumping and spraying.

Summary of the Invention

Accordingly, the present invention is a carrier comprising a ceramic powder having an average particle size in the range of 0.5 micrometer (0.5 micron) or less and the amount of the total solid content in the range of 30% by volume or less, of water and a surface stabilizer of 0.5 to 5% by weight of the ceramic powder. A method of preparing a ceramic composition by suspending in a fluid is provided. At least 1% by weight of anionic or cationic dispersant based on the ceramic powder is added to the suspended material. Dilution of the suspension and dispersant with water then gives an apparent viscosity of less than 30 dyn · s / cm 2 (3000 centipoise).

In another embodiment, up to 12% by weight of organic binder, preferably 3 to 12% by weight, is added to the suspension to prepare a slip composition. Slips are then applied to the substrate or mold to produce an untreated layer having a pore size of less than 0.5 micrometers (0.5 microns).

The above features and advantages of the present invention are exemplary, but are not limited thereto. Other advantages and features of the present invention will become more apparent while reviewing the detailed description of the invention.

To produce a dense thin layer of ceramic or dielectric powder, such as BaTiO ₃ , from an aqueous suspension of ceramic powder, an apparent viscosity low enough to prevent sedimentation at high solids content and to be processable, ie to cast or pour the thin film Level, having a Bingham yield point that achieves a gel state where the applied suspension layer does not expand and optionally contains an organic binder that holds the particles together during subsequent operations in the process before the ultimate high temperature sintering operation. It is necessary to produce a stable suspension.

A further feature of the present invention is to provide a very thin coating on the particles, which is virtually more hydrophobic and helps to control the properties of the untreated layer with an organic binder, creating a zeta potential that weakens the intrinsic interparticle attraction. .

In order to produce suspensions and slips containing an increased content of ceramic powder in an aqueous carrier fluid, the inventors have provided surface stabilizers that result in reduced aggregation and more uniform pore size distribution in the untreated layer and the green body produced therefrom. It has been found that there is a critical concentration range for. In one embodiment, up to about 30% by volume, more specifically 20 to 30% by volume, of ceramic powder is uniformly suspended in an aqueous carrier fluid of deionized water previously added with a surface stabilizer to prepare a ceramic composition for tape preparation. . The term "homogeneous" means that the pore size formed in the untreated layer prepared from the suspension or slip of the present invention is 0.5 micrometer (0.5 micron) or less. The prepared suspension has a consistency similar to fluid to paste depending on the content of the ceramic powder. Has Dispersant is then added to the mixture to obtain a uniform suspension. Although various ceramic powders are well known to those of ordinary skill in the art, the passivation-dispersion technology in the most advantageous powder from powder or from 4 to pH in the range of about 11 [instability under the presence of water 10 ^-4 M to ^{10 At least one} of the metal components of the ¹ M ceramic powder is a powder having a relatively high solubility or leaching property. Also, one or more metal components having an average particle size of 0.5 microns (0.5 microns) or less, preferably between 0.05 microns (0.05 microns) and 0.5 microns (0.5 microns) (and in the solubility or leaching ranges described above). Powders) are most advantageous in terms of the surface stabilization-dispersion techniques described herein.

Many methods for measuring the average particle size of ceramic powders are well known to those of ordinary skill in the art. In the present invention, the average particle size was measured by BET gas adsorption surface area analysis. This method is particularly useful for calculating the average particle size when the powder particles are substantially spherical as in the case of the powder used in the present invention.

The term ceramic powder further includes metal oxides such as zinc oxide, bismuth oxide or aluminum oxide; Metal sulfides, metal borides, metal nitrides, metal carbides, metal tellurides, metal arsenides, metal silicides, metal selenides and metal halides, and mixed materials such as metal titanates, metal tantalates , Metal zirconates, metal silicates, metal germanates, and metal niobates.

The metal component of the metal oxide includes metals belonging to groups IIA to IIB in the periodic table of the elements, and also includes lanthanum and actinium series.

Ceramic powder is further defined as comprising complex oxides having the formula ABO ₃ , wherein A consists of one or more of metal species having similar ionic radii and ionic charges, and includes barium, calcium, magnesium, lead, strontium , And zinc. Group B consists of one or more metals selected from the group consisting of hafnium, tin, titanium, zirconium, and may further contain mixtures or solid solutions thereof. Those skilled in the art will recognize the similarity of the cited species B with titanate based on reported values for ionic radius and ionic charge.

In another embodiment, the ceramic powder is further defined as containing a complex oxide as defined above having the formula ABO ₃ , and may also contain one or more doping materials. The addition of the dopant generally does not affect the properties of the slip or suspension when the amount of the dopant added is typically a small percentage by weight of the total solids. Therefore, it will be appreciated by those skilled in the art that various "dope materials" may be used. The term "dope material" is defined to include additives that are used to tailor the electrical performance of the ceramic powder in the finished capacitor. In the present invention, the doping material is aluminum, antimony, bismuth, boron, calcium, cadmium, chromium, copper, cobalt, hafnium, iron, lanthanum, lead, manganese, molybdenum, neodymium, nickel, niobium, praseodymium, samarium, scandium, silicon, It may be defined to include at least one metal selected from oxides of the group consisting of silver, tantalum, titanium, tin, tungsten, vanadium, yttrium, zinc and zirconium.

The surface stabilizer is (iii) completely burned cleanly from the suspension or slip at a temperature of about 1050 ° C. or less, (ii) provides a uniform surface charge on the ceramic particles as a function of carrier fluid pH, and (iii) 4 to about Has a reasonably uniform solubility over a pH range of 11, (i) forms a relatively insoluble precipitate with one or more metal species of the ceramic powder, (i) promotes adsorption of the desired anionic or cationic dispersant, ) Adsorption of dispersant, hereinafter, refers to a sol that remains opaque for a period of one week without detectable precipitation as compared to a control sample prepared in an aqueous carrier having the same solids content but no surface stabilizer. It can be any acid or base with defined “improved settling properties”. Analytical methods for measuring the opacity of the sol are known to those of ordinary skill in the art and are not described in detail herein.

Many surface stabilizers are known to those of ordinary skill in the art, but particularly preferred surface stabilizers may include compounds or mixtures of succinate, benzoate, formate, couferon and 8-hydroxyquinoline. Although not wishing to be so limited, oxalic acid is the preferred surface stabilizer as discussed and is evaluated in the examples provided below. Preferably, oxalic acid is dissolved in deionized water at 1-3% by weight of the ceramic powder.

The inventors also found that, with respect to ceramic powder content of up to 30% by volume, the optimum surface stabilizer content is 1 to 3% by weight when the dispersant amount is 1% by weight or more. At lower concentrations of surface stabilizers, ceramic powders begin to form aggregates. At higher concentrations, excess surface stabilizer in the carrier fluid forms precipitates with lean metals and dispersants, and the apparent viscosity is at an unacceptably high level, i.e. 30 dyn.s / when measured at 50 to 100 / sec. Increased to a level greater than 2 cm 2 (3000 centipoise). The term "apparent viscosity" is known to those of ordinary skill in the art and may be defined below as a value obtained by fitting as a function of detection for a viscosity-shear rate curve made from actual viscosity measurements. The resulting function can be used to calculate the viscosity at shear rates between 50 and 100 sec ⁻¹ . The point-slope method is then used to extrapolate to a shear rate of zero using a linear fit to the viscosity-shear rate curve to determine the apparent viscosity.

The present invention may use a dispersant concentration of at least 5% by weight depending on the binder and surface stabilizer selected for a given slip composition.

Although not limited thereto, the dispersant is preferably (i) compatible with the surface stabilized ceramic powder particles and uniformly coating the particles, and (ii) above the particle surface rather than extending radially therefrom. Preferably having a train drawn in a parallel manner, (i) minimizing crosslinking or "salt" in the bulk suspension, and (iii) in excess of +10 millivolts relative to the above-mentioned content. Includes the property of a polymer having a zeta potential in the range of +10 millivolts to about +40 millivolts or in the range of -10 millivolts to about -40 millivolts. Zeta potential sizes below ± 10 millivolts result in suspensions with insufficient electrostatic repulsion to prevent particle agglomeration.

Various anionic and cationic surfactants having a molecular weight of less than 1000 to more than 30,000 are used as dispersants. Examples include natr, potassium, or preferably ammonia salts, lauryl sulfate, alkyl polyphosphates, dodecyl benzene sulfonates, diisopropylnaphthalene sulfonates, dioctylsulfosuccinates, ethoxylated and lauryl sulfides of stearates Alcohols, and ethoxylated and sulfided alkyl phenols.

Various cationic surfactants include polyethyleneimine, ethoxylated fatty amines and stearylbenzyldimethylammonium chloride or nitrate. Other dispersants intended for the present invention include polyethylene glycol, lecithin, polyvinyl pyrrolidone, polyoxyethylene, isooctylphenyl ether, polyoxyethylene nonylphenyl ether, amine salts of alkylaryl sulfonates, polyacrylates and related salts , Polymethacrylates and related salts, and fish oils. Additional anionic and cationic dispersants having the above properties are referenced in the title "McCutcheon's, Volumes 1 and 2, McCutcheon Division" published by The Manufacturing Confectioner Publishing Co. You can find it at

In operation, up to 30% by volume of ceramic powder is suspended in an aqueous carrier fluid containing from 0.5 to 5% by weight surface stabilizer. A dispersant of at least 1% by weight of ceramic powder is then added to the surface stabilizer containing carrier fluid. An additional amount of water is then added to achieve the stated weight percent content.

A final suspension pH of about 4 to about 11, preferably 7 to 10, is obtained. Suspensions prepared in this way have a Bingham yield point of less than 230 dyn / cm 2 and an apparent viscosity of less than 30 dyn · s / cm 2 (3000 cps).

The inventors found that adding the surface stabilizer to the carrier fluid prior to adding the ceramic powder is important for the performance of the suspension or slip as an untreated layer. While not wishing to be bound by any particular theory, it is believed that dissolution reactions on the powder surface occur rapidly, which requires that the surface stabilizer be available when the particles are introduced into the carrier medium. If the surface stabilizer is added after the powder has been introduced, precipitation is very likely to occur in the bulk solution rather than at the particle surface.

In alternative embodiments, an amount of dispersant may be added directly to the carrier fluid with the surface stabilizer prior to the addition of the ceramic powder.

In the process for producing slips of ceramic powder, up to 12% of the organic binder is added to the suspension prepared according to the method described above and further diluted with water.

The criterion for selecting the binder is that the binder should be uniformly dispersed throughout the suspension and combined with the surface stabilized or dispersant coated ceramic particles while minimizing the separation of the phases. Uniform distribution of surface stabilized particles facilitates particle coating with the binder, and therefore smaller amounts of binder are used. Although not limited to this, polyethylene glycol commercially available under the trade name "Carbowax ^(R )" was used. Carbowax is a trademark of Union Carbide of Danbury, Connecticut. In another embodiment, polyvinylpyrrolidone was used as the binder in a content of 12% by weight of ceramic material. In another embodiment, a total of 13% polyethyleneimine was used as mixed dispersant and binder.

The slip material prepared at the above-described content level was then applied onto the substrate by a method known in the art to prepare an untreated layer having a thickness of 5 micrometers (5 microns) or less.

A green body can be prepared by sandwiching a conductor layer between a plurality of untreated layers. One of ordinary skill in the art is familiar with the techniques for making the green body, and therefore the technique will not be discussed further.

1A and 1B, scanning electron micrographs obtained from suspensions prepared according to Example 1 are shown at two different magnifications. The content of 0.5% by weight of oxalic acid and 1% by weight of polyethyleneimine was used. As shown, the aggregated area can be clearly seen. Significant improvements in cohesiveness were seen in the micrographs of FIGS. 2A and 2B and FIGS. 3A and 3B in which untreated layers were prepared according to the methods of Examples 2 and 3. A content of 0.5% by weight of oxalic acid and 1% by weight of oxalic acid and 1% by weight of polyethyleneimine was used at 5% by weight of polyethyleneimine. 4A and 4B are micrographs of the cast unprepared layer prepared according to Example 5 using 1% by weight surface stabilizer and 3% by weight polyethylenimine. When the amount of polyethyleneimine was increased to 5% by weight, an untreated layer shown in FIGS. 6A and 6B similar to FIG. 5 was obtained. When 2 to 3% of oxalic acid and 1 to 5% of polyethyleneimine were used (FIGS. 7 to 9), a commercially acceptable untreated layer was obtained. However, the micrograph of FIG. 1 shows that excessive flocculation and inoperable viscosity were obtained when using 0.5% by weight of oxalic acid content and 1% by weight of polyethyleneimine at a solid content of up to 30% by volume. Micrographs demonstrate the importance of the lower range of surface stabilizer content for aqueous suspensions. While not wishing to be bound by any particular theory, this demonstrates that the surface stabilizing effect of oxalic acid is insufficient to surface stabilize the barium titanate of the indicated solid content at 0,5% by weight.

Referring now to FIG. 10, an aqueous slip was prepared according to the method described in Examples 16 and 17, wherein 3% by weight of oxalic acid and 1% by weight of polyethyleneimine were mixed with 3% by weight of polyethylene glycol binder. The micrographs shown in FIGS. 10A and 10B show that the surface of the untreated layer has a uniform pore size distribution of 0.5 microns (0.5 microns) or less.

In FIG. 11, an aqueous slip was prepared according to the method described in Example 18, in which 3% by weight of oxalic acid and 1% by weight of polyethyleneimine were mixed with 6% by weight of polyethylene glycol binder. A commercially acceptable untreated layer having a pore size of 0.5 microns (0.5 microns) or less was obtained.

In Figure 12, an aqueous slip was prepared according to the method described in Example 19 where 3% by weight of oxalic acid and 1% by weight of polyethyleneimine were mixed with 12% by weight of polyvinyl pyrrolidone binder. A commercially acceptable untreated layer having a pore size of less than 0.5 microns (0.5 microns) was obtained.

In FIG. 13, an aqueous slip was prepared according to the method described in Example 20 where 3% by weight of oxalic acid and 2% by weight of polyethylenimine were mixed with 11% by weight of polyvinyl pyrrolidone binder. An apparent viscosity of 10.5 dyn · s / cm 2 (1050 cps) was obtained.

In FIG. 14, an aqueous slip was prepared according to the method described in Example 21 where 3% by weight of oxalic acid and 1% by weight of polyethyleneimine were added as a dispersant. An additional 12% by weight of polyethylene imine was added as binder. An apparent viscosity of 7.79 dyn s / cm 2 (779 cps) was obtained. The prepared untreated layer had a pore size of 0.5 micrometers (0.5 microns) or less.

The invention will be more readily understood by the following non-limiting examples. The apparent viscosity and content for Examples 1-21 are summarized in Table 1 below. % Is the weight percent of ceramic powder unless otherwise stated.

<Example 1>

An aqueous solution of oxalic acid was prepared with 0.2810 g of oxalic acid (H ₂ C ₂ O ₄ .2H ₂ O) and 23.2 g of H ₂ O. 56.8068 g of barium titanate BT-10 having an average particle size of about 0.1 micrometers (0.1 micron), manufactured by Applicant Cabot Corporation, is slowly added to the oxalic acid solution with high shear mixing (typically 5000 rpm). It was. About 1.1433 g of 50% "PEI" or polyethyleneimine prepared by Kodak in water was added to the oxalic acid / barium titanate suspension at the same mixing shear rate as described above. The final suspension contained 0.5% oxalic acid and 1% PEI. The suspension obtained had an unacceptably high apparent viscosity in excess of 30 dyn · s / cm 2 (3000 cps), and therefore is not suitable for producing an untreated ceramic layer by wet lay-down technique.

Actual viscosity measurements were performed on the suspension at 25 ° C. using a cone-plate viscometer at shear rates ranging from 0.6 to 120 sec ⁻¹ . If the measured viscosity of the suspension is beyond the range recognized by the measuring head (had) of the viscometer or if insufficient data points are obtained to observe the plateau region for the viscosity-shear velocity plot, the suspension viscosity is set to "NA. ". The cone plate viscometer was a Digital Viscometer of the Model # LVTDCP or Model DV-III physical system manufactured by Brookfield Engineering Laboratory, Inc., Stafton, Massachusetts. .

All suspensions for which rheological data were obtained were pseudoplastic. In addition, many suspensions exhibited a Bingham yield stress, below which no slurry flowed. The latter property is desirable for most tape or layer forming methods to prevent the slurry from flowing out of the substrate after deposition. Bingham yield points were obtained by recording the shear stress at which the suspension or slurry tested was also tested at the point where no flow chart is shown using the minimum shear rate equal to 0.6 sec ⁻¹ .

<Zeta potential test method>

An amount of suspension or slip prepared according to the examples was measured for zeta potential on Brookhaven ZetaPlus manufactured by Brookhaven Instruments Corporation, Holtsville, NY.

<Production of Untreated Layer>

An untreated layer of suspension or slip was prepared by the following method:

A suspension or slip of about 2-3 cc was placed on the glass side and manually dispersed by operating a metal blade thereon to obtain a uniform thickness. In another method, the passive doctor blade was operated on the deposited suspension and slip material. The suspension was then dried at room temperature for 10-15 minutes to prepare an untreated layer.

<Examples 2 to 15>

This example was prepared according to the method of Example 1 using the amounts of reactants shown in Table 1. Table 1 shows the weight percent and apparent viscosity values of oxalic acid as surface stabilizer and polyethyleneimine as dispersant obtained in the final suspension.

<Example 16>

An aqueous solution of oxalic acid containing oxalic acid _{(H 2 C 2 O 4 ·} 2H 2 O) 1.7068 g were prepared for H ₂ O 20.0468 g. 56.8370 g of Cabot B-10 barium titanate was slowly added to the oxalic acid solution with high shear mixing (usually 5000 rpm). 1.1349 g of polyethyleneimine (50% PEI prepared by kodak in water) was added to the oxalic acid / barium titanate suspension under the same mixing shear as described above. Then 1.6778 g of the binder (Carbowax PEG 1450F, Uni-Carbide Co., Ltd.) was added to the suspension. The final slip contained 3% oxalic acid, 1% PEI and 3% binder as compared to the total 69.82% by weight (28.63% by volume) for the barium titanate powder. The slip was shear decremented to have an apparent viscosity of 4.28 dyn · s / cm 2 (428 cps). An untreated layer was prepared according to the method of Example 1.

<Examples 17-21>

This example was prepared according to the method of Example 16 using the amount of reactants shown in Table 1. Table 1 shows the weight percent and apparent viscosity values of oxalic acid as surface stabilizer and dispersant obtained in the final suspension. The dispersant used in Examples 19 and 20 was polyvinyl pyrrolidone, available as PVP K-30 from GAF Corporation, Wayne, NJ. In Example 21, polyethyleneimine at a concentration of 1% by weight was used as a dispersant and 12% by weight was used as the binder. The untreated layer was prepared by the doctor blade method provided in Example 16. As is apparent from Table 1, both the apparent viscosity and the Bingham yield point values were in an acceptable range for commercial use.

TABLE 1

Effect of Composition on Viscosity

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Claims (20)

Contains ceramic powders containing at least one metal component, suspended uniformly in an aqueous fluid in the range of up to 30% by volume total solids in suspension, with an average particle size of less than 0.5 micrometers, The ceramic powder is coated with an insoluble precipitate formed from a surface stabilizer and the at least one metal component, Contains at least 1 wt% dispersant of the ceramic powder, Ceramic suspension having an apparent viscosity of less than 3 × 10 ⁻⁶ MPa · s (3000 cps). 2. The ceramic powder of claim 1, wherein A is at least one metal selected from the group consisting of barium, calcium, magnesium, lead, strontium, and zinc, and B is 1 selected from the group consisting of hafnium, tin, titanium, and zirconium. A composite metal oxide having the formula ABO ₃ which is a metal of at least two species, or a mixture or a solid solution thereof, a ceramic suspension. 3. The ceramic suspension of claim 2 wherein said composite metal oxide is barium titanate. The ceramic suspension of claim 1 wherein said surface stabilizer is selected from the group consisting of succinate, benzoate, formate, couferon, 8-hydroxyquinoline, oxalic acid, and mixtures thereof. The method of claim 1, wherein the ceramic powder is uniformly suspended in the aqueous fluid in an amount of 17.72 to 30% by volume, and the apparent viscosity of the suspension measured at 25 ° C. and shear rate in the range of 0.6 to 120 sec ⁻¹ is 3 A ceramic suspension of less than 10 ⁻⁶ MPa · s (30 dyn · s / cm 2). The method of claim 3, wherein the composite metal oxide is aluminum, antimony, bismuth, boron, calcium, cadmium, chromium, copper, cobalt, hafnium, iron, lanthanum, lead, manganese, molybdenum, neodymium, nickel, niobium, praseodymium, samarium And at least one doping material selected from the group consisting of scandium, silicon, silver, tantalum, titanium, tin, tungsten, vanadium, yttrium, zinc and zirconium. The ceramic suspension of claim 1, wherein the zeta potential of the ceramic powder is +10 to +40 millivolts or -10 to -40 millivolts. The ceramic suspension of claim 1, wherein a Bingham yield point of the suspension is less than 2300 N / m ³ (230 dyn / cm 3). The ceramic suspension according to claim 1, wherein the solubility of the metal component in the fluid is 10 ⁻⁴ to 10 ⁻¹ mol / liter. The ceramic suspension of claim 1 further comprising a predetermined amount of an organic binder. A ceramic powder comprising at least one metal component and an average particle size of the powder of less than 0.5 micrometers is mixed with an aqueous fluid containing from about 0.5 to about 5 weight percent surface stabilizer of the ceramic powder up to 30% by volume of solids, Coating the ceramic powder with an insoluble precipitate formed from a surface stabilizer and the at least one metal component, A process for producing a ceramic suspension having an apparent viscosity of less than 3 × 10 ⁻⁶ MPa · s (3000 cps), comprising mixing at least 1 wt.% Dispersant of the ceramic powder with the suspension. 12. The ceramic powder of claim 11 wherein A is at least one metal selected from the group consisting of barium, calcium, magnesium, lead, strontium, and zinc, and B is selected from the group consisting of hafnium, tin, titanium and zirconium. A composite metal oxide having the formula ABO ₃ , which is at least one metal, or a mixture or solid solution thereof. The method of claim 12, wherein the composite metal oxide is barium titanate. The method of claim 11, wherein the surface stabilizer is selected from the group consisting of succinate, benzoate, formate, couperone, 8-hydroxyquinoline, oxalic acid, and mixtures thereof. The suspension according to claim 11, wherein the suspension has an apparent viscosity of less than 3 × 10 ⁻⁶ MPa · s (30 dyn · s / cm 2) measured at a shear rate in the range of 25 ° C. and 0.6 to 120 sec ^−1. Adding an additional amount of aqueous fluid to the. The method of claim 13, wherein the composite metal oxide is aluminum, antimony, bismuth, boron, calcium, cadmium, chromium, copper, cobalt, hafnium, iron, lanthanum, lead, manganese, molybdenum, neodymium, nickel, niobium, praseodymium, samarium And at least one doping material selected from the group consisting of oxides of scandium, silicon, silver, tantalum, titanium, tin, tungsten, vanadium, yttrium, zinc and zirconium. The method of claim 11, wherein the zeta potential of the ceramic powder is +10 to +40 millivolts or -10 to -40 millivolts. The method of claim 11 wherein the Bingham yield point of the suspension is less than 2300 N / m 3 (230 dyn / cm 3). The method of claim 11, wherein a predetermined amount of organic binder is added to the ceramic suspension to form a slip composition. The method of claim 11, wherein the solubility of the metal component in the fluid is 10 ⁻⁴ to 10 ⁻¹ mol / liter.

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